use -F no grep
$ cat test.txt
"Limit reached."[\n]"
test
"Limit reached."[\n]"
$ grep -F '"Limit reached."[\n]"' test.txt
"Limit reached."[\n]"
"Limit reached."[\n]"
De acordo com a página "Manual",
-F, --fixed-strings, --fixed-regexp Interpret PATTERN as a list of fixed strings, separated by newlines, any of which is to be matched. (-F is specified by> POSIX, --fixed-regexp is an obsoleted alias, please do not use it new scripts.)